A representative previous invention includes U.S. patent application Ser. No. 10/284,873 to Warman et al. entitled, “Addressing Recurrent Atrial Fibrillation,” the contents of which are incorporated herein by reference. As is know, some heart patients experience episodes of atrial tachyarrhythmia, including atrial fibrillation and/or atrial flutter (AF). Although AF episodes may not be immediately life-threatening, AF episodes may be associated with extreme symptoms, a reduced quality of life, and a reduced cardiac output. For heart patients having a multi-chamber pacemaker, AF episodes present an additional problem, in that the pacemaker may coordinate ventricular pacing with atrial activity. When an AF episode begins, it is undesirable for ventricular pacing to be timed according to atrial activity. Accordingly, some pacemakers are equipped with a “mode switching” capability. The principal purpose of such mode switching is to prevent the pacing system from delivering ventricular paces that track atrial activity when the atrium experiences an episode of atrial tachycardia. When the atrial rate is normal, the pacemaker assumes a tracking mode, such as DDD/DDDR, in which ventricular pacing tracks atrial activity. When an AF episode occurs, however, the pacemaker mode switches to a non-tracking mode, such as DDIR, and paces the ventricle independently of atrial activity.
When an AF episode occurs, the pacemaker or another medical device may apply therapy to terminate the AF episode. Therapy may comprise application of a cardioversion shock or administration of drug. Another therapy for atrial tachycardia is overdrive pacing of one or both atria, in which the pacemaker delivers pacing therapy at a rate faster than the then-present intrinsic rhythm. Overdrive pacing is often effective in disrupting an atrial arrhythmia such as AF and terminating the episode. Of course, an AF episode may also terminate spontaneously.
It has been observed that a recurring AF episode may occur within seconds or minutes after the termination of the first AF episode, and herein such an episode is referred to an early recurring AF (ERAF) condition. Although an ERAF episode does not always follow the termination of a preceding AF episode, it has been demonstrated clinically that a patient may have an increased risk of a recurrent AF episode for a period of time following a prior AF episode, both an initial and an ERAF episode. This phenomenon has been attributed to the fact that the local refractory period after AT is temporarily shortened, causing the substrate to be vulnerable to premature atrial beats which will re-induce AT/AF. In patients with AT/AF, who have a pacemaker implanted, atrial overdrive pacing may influence mechanisms which are held responsible for the early recurrence of AT/AF, including long pauses following premature beats, the number of premature beats, and the temporal dispersion of the refractory period. Some preliminary results have demonstrated a benefit of overdrive pacing. However, continuous overdrive pacing may not be well tolerated in the long term.
Therefore, with the Post-Mode Overdrive Pacing (PMOP) algorithm operational, overdrive pacing in the atrium is only activated in the phase shortly after a previous AF episode, when the tissue is vulnerable for premature beats to induce AT/AF. PMOP prevents AT/AF recurrence during the active phase of overdrive pacing. However, in this active phase only half of the AT/AF recurrences occur (31%), while half of the episodes are missed (29%) before PMOP is activated. The efficacy may be increased by preventing the episodes between device confirmed termination and before overdrive pacing is activated. Even more episodes can be prevented by overdrive pacing immediately when sinus rhythm occurs without waiting for device confirmed termination. Thus the clinical relevance of overdrive pacing could be improved theoretically at least a factor two. Based on the results of this study a new algorithm PLOP (Post-Long pause Overdrive Pacing) has been developed and tested in a clinical research study.